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Thursday, April 30, 2009

I've been slowly gathering these up over the last few weeks...and there will be more...but because we've been looking at ophiuroids this week...I thought it would be cool to introduce it here!! I hope to have one for each living echinoderm group along with some other miscellaneous ones....

Some basket stars, such as Gorgonocephalus have arms that will reach almost 2 to 3 feet across! Not all of them are this big but a lot of them are pretty sizeable....2. Ophiopsammus maculata (New Zealand)
A member of the Ophiodermatidae, which are usually pretty small tropical beasts..but this one gets pretty big!

A disk that is about 2-3 inches across with an impressive arm span of over 6 to 7 inches!!

Its unclear how they feed but some suspect that they do something very similar to this!3. Astrostoma agassizi (Antarctic: Southern Ocean)
Okay, so, I'm cheating. Because Astrostoma agasszi IS a member of the Gorgonocephalidae (see above).
I will probably write this up in more detail later but here's some quick details at this site:

Astrotoma is BIG. Disk is easily 2-3 inches across with correspondingly thick arms.

They live in the Southern Ocean/Antarctica in relatively deep-water (about 90-1500m) and feed on crustaceans and other various prey using their very long arms!

4. Ophiarachna incrassata: Giant Green Fish-eating Brittle Star (tropical Indo-Pacific) I wrote up something about this species awhile back There's a lot of neat things to say about it..but it is BIG. check this video out again!5. Ophiocoma aethiops (Baja California/Mexico)
All members of the genus Ophiocoma are tropical, shallow-water in all of the world's oceans and all of the species are pretty sizeable. But for some reason, Ophiocoma aethiops from tropical East Pacific is just a bit bigger then the others species of Ophiocoma that one sees in the Indo-Pacific. There's more to this beast..but for now..just appreciate the fact that its a BIG one!Honorable Mention: Stegophiura ponderosa
So, this is a deep-water species (at least 100-500 m) from off the west coast of North America, Japan, and Russia.

It turns out that crinoids will stay in the same place for A LONG TIME (although some may not come out until the sun goes down).

Some are known to stay in the same place for up to TWO years!!!

One account actually reported a crinoid that stayed in the same "residence" for FIVE years!!

Some observations series have continued for over SIX MONTHS with no apparent change!

Wilson observed 13 mariametrid crinoids on a total of 11 perches. There were some individuals that "left" and returned but on the whole...

She observed over the 59 day period that 80% of the crinoids continued to occupy their original perches!

Big feeding clusters like this one have interesting dynamics. Its thought that these big bunches may improve feeding efficiency by slowing down water currents. Big individuals tend to be solitary whereas a bunch of smaller ones will aggregate.

But apparently, there IS competition among individuals for a specific perch with a "winner" forcing the "loser" from the most ideal perch.

So, what have we learned?Crinoids apparently stay in a SINGLE place and they will work to stay there.Wow. Who'd a thot something so innocuous what have so much depth?

Monday, April 20, 2009

Today..the SECRET LIVES of FEATHER STARS! (HINT: wait for the twist at the end!)

In many ways, feather stars (aka crinoids-owing to their membership in the Class Crinoidea) are among the most mysterious of echinoderms. We know them as fairly stationary flower-like animals that feed passively as water currents flow by them...

So what happens after that?? Pictured here is a series of what happens!!! The doliolaria settles and begins to TRANSFORM!!! Into this sort of weird transition before it becomes a weird protolarvae called a cystidean larvae!!Here, we have ACTUAL photos of an Australian crinoid-Aporometra wilsoni showing various transitionary larval stages:

But WAIT!! The cystidean larvae doesn't look at all like the weird feathery thing we started with....It looks more like this: a STALKED crinoid!!!

To recap: TWO KINDS of crinoids are alive today.

"Unstalked" crinoids are those which are basically a skeletal cup with a bunch of arms, sometimes with little "legs" called cirri. The great majority of crinoids alive today...especially in tropical shallow-water or in many cold-water settings are unstalked or "comatulid" crinoids.

BUT.....

There exists a much older crinoid body form known as the STALKED crinoids which are seen primarily in the Paleozoic fossil record and today live in the minority in largely deep-sea environments.

Keep that in mind...and let's get back to the story...

As the cystidean larvae gets larger it actually starts to develop a base, a stalk and a feeding cup...But THEN, the as the larvae grows, the TOP cup part??? It starts to form little cirri/legs and as it gets bigger and bigger...the cystidean starts to look more like a little tiny stalked crinoid.

Once the feeding arms and etc. have become fully formed..it reaches what's called the pentacrinoid stage.

(pentacrinid courtesy of Greg Rouse-SIO)

The top, cup segment of the pentacrinoid stage develops until this happens:

(note that in the real world the crinoid pentacrinoid stage does not go "BOOM!")

The little cup matures and BOOM!! It separates from the stalk!! and the "cup" is what we see as the adult stage of the "unstalked" crinoids!!Neat, eh?

And on top of that is an important evolutionary lesson. "Unstalked" crinoids are DESCENDED from Stalked crinoids!!

We see the ancestry of these animals in their life cycle!!The thing with crinoids? the lessons are subtle but VERY rewarding!
(special thanks to Jodie Haig & Greg Rouse for the images!)

This has been an ambitious project to catalog ALL of the Antarctic and subAntarctic marine invertebrates (including but not limited to corals, jellies, worms, crustaceans, mollusks, and of course...echinoderms!) which have been collected under the auspices of the USARP since 1963 and housed in Washington DC in the collections at National Museum of Natural History! This project is of course, supported by the NMNH and the National Science Foundation!!

Monday, April 6, 2009

Well, one of the big shocks to most people is when I tell them that many species of the ever-humble sea star don't just settle for frakkin' mussels and clams..they actually GOES for the big, moving prey! shrimps, fishes and..?????

The"Cryptic" Predator

In New Zealand there lives this weird thing called Stegnaster inflatus (Asterinidae)

For a starfish, Stegnaster has a really odd feeding mode. It sits up on its tippy toes as seen above and pretends to be a cave or some other crevice.

(From Michel Jangoux's Echinoderm Nutrition)

Following the diagram above, once some small prey has situated itself inside the "cave" with the body lifted above on its arm tips (A), followed by the star then slowly closing off the edges (C and D) until finally whatever is inside gets trapped and the cardiac stomach drops on the hapless prey (E)!! digesting it alive!!

According to Anthoni's Seafriends page this is effective not only against shrimps and snails, but also seahorses and other small fishes!!!

Active Predators When I say active, I mean, they actually use a specific structure for feeding on and obtaining prey....Many of these species practice some kind of bottom-water column type feeding.

1.Stylasterias forreri
Probably one of the first sea stars to be observed feeding or catching moving prey, this animal gained notoriety quickly as being the "fish eating" starfish.

The surface of this fairly large animal (diameter gets up to almost 1.5 feet across!) are covered with fairly large pedicellariae (teeth-like jaws) with many big jagged hooks that are deployed on batteries around all of the spines and are deployed as big grabby claws whenever food is detected.

I suspect that the Styla part ofStylasterias refers to "stylet"alluding to the sharp spines on the body surface.

Try as I might, I could not locate a photo or a picture of Stylasterias actually capturing a fish, so we here at the Echinoblog looked to our Echinoblogical Art Department to delivery a hypothetical rendering of this behavior:

(note that the fish (aka Sea Kitten) is probably not suffering nearly as much as it appears in the rendering!)

These animals live off the west coast of North America in fairly deep-water (about 100-800 m) and were the among the most recently reported to feed on mobile prey ina cool paper byLynn Lauerman who observed them with ROVs and had many great opportunities to collect and watch them alive.

Although they have opportunistic tendencies (they don't always feed on mobile crustaceans) they do show a very strong propensity for eating things that swim by them..3. Labidiaster annulatusI wrote a fairly involved post about this really neat Antarctic predator here. But short version...it uses its huge and jagged pedicellariae:To feed on krill as they go swimming by it. Prey get held fast by these jagged jaws and are dragged down to the mouth where they are eaten alive!Aieee!!

4. The Brisingids!

Shown here is Novodinia antillensis from the NOAA explorer site) Taken by S. Brooke.

I wrote a much more involved post about these neat animals here. But, but the short version is that brisingid asteroids are suspension feeders/predators that feed by using pedicellariae all over their arm spines to capture prey as the water current takes food through their arm "feeding basket" providing foodstuffs to be captured on the arm spines.

How do Starfish EAT??? And why am I suddenly writing about this???? The other day, an educated but non-professional person wrote something to me that said "All starfish eat mussels".

This was followed by me doing this:Then...I regained my composure.

Okay..so let me say this again. NOT ALL STARFISH EAT MOLLUSKS!!

There seems that YEARS of biology and zoology textbooks using the common nearshore asteriid starfish Asterias and Pisaster and their kin as models of the "common" starfish have led to assumptions and misconceptions about their feeding mode as the basis for ALL starfish.STARFISH DO NOT FEED ALIKE. There is a HUGE diversity of feeding modes among asteroids.
Let's survey some diversity and break some overgeneralizations shall we???1. SOME Starfish DON'T use a stomach to feed!

Paxillosidans: including "sand stars" such as Astropecten and/or Luidia will usually SWALLOW their prey whole.

...and others SWALLOW mud and the foodish bits that are found in deep-sea mud and sediment! No eversible stomachs here.Many deep-sea (these live at 3000+m !!) porcellanasterid "mud stars" are collected with their guts FILLED with mud.

To the point that the animals are literally BALLS of mud surrounded by starfish stuff!! The thickness you see in this deep-sea Styracaster sp?? ALL MUD!!!2. And then, we get to those starfish that DO feed using their extendable stomachs!

Many, such as the tropical sea star Protoreaster gain most of their nutrition from microalgae and don't really feed much on meaty bits (which is probably why they don't live long if you feed them clam meat)and this Patiria miniata extend their stomachs in order to feed on small microalgae or opportunistically ANY small food they can roll their stomach over and eat!! Usually starfish species that feed in this way can also feed on encrusting animals like sponges, bryozoans, and etc...This feeding mode is actually pretty common.

If I could make ANY generalization about starfish feeding, it is that many species are OMNIVOROUS. That is, they can feed on just about anything slower then them..algae, encrusting invertebrates, etc. But really, they don't always feed on other moving animals

...and finally we get to the starfish that FEED on bivalve mollusks. Many of these are taxa that are restricted to the ASTERIIDAE. and EVEN these starfish don't always feed on bivalves...sometimes its snails or what have you... To be honest, there's a fair number of asteriid species that feed this way..but

Its a specialized feeding mode (the humped posture over the shell)

The great majority of taxa aren't asteriid starfish and DON'T feed this way.

So, what ELSE do starfish EAT (i.e., prey on vs. just opportunistically feed on)?(this is just a survey of prey items..and NOT a complete listing!)

NUDIBRANCHS! (Cadlina luteomarignata being fed upon by Crossaster papposus-contrary to what the original source says)

About Me

I pursue starfish related adventure around the world with a critical eye and an appreciation for weirdness.
Support has been courtesy of the National Science Foundation but the views and opinions presented herein are mine and do not reflect the opinions of them or any affiliated institutions.
Need to hire an invertebrate zoologist/marine biologist? Please contact me!